Symmetries of power-free integers in number fields and their shift spaces

Abstract

We describe the group of $\mathbb{Z}$-linear automorphisms of the ring of integers of a number field $K$ that preserve the set $V_{K,k}$ of $k$th power-free integers: every such map is the composition of a field automorphism and the multiplication by a unit. We show that those maps together with translations generate the extended symmetry group of the shift space ${\mathbb{D}}_{K,k}$ associated to $V_{K,k}$. Moreover, we show that no two such dynamical systems ${\mathbb{D}}_{K,k}$ and ${\mathbb{D}}_{L,l}$ are topologically conjugate and no one is a factor system of another. We generalize the concept of $k$th power-free integers to sieves and study the resulting admissible shift spaces.

minor changes, added Theorem 5.13; to appear in Israel J. Math